Try a different WiFi channel (that’s if you are using WiFi) or perhaps wire thd left speaker, if practicable. 
You could also try unpairing the speakers and checking for any updates and then try pairing them the other way around - swapping their position in the process.

If using WiFi, select a ‘fixed’ non-overlapping channel 1, 6 or 11 for your routers 2.4Ghz WiFi band and set the channel-width to 20Mhz only.

If using a wired setup for Sonos, rather than WiFi, then in addition to the router settings suggested above, set any SonosNet channel in the Sonos App to a completely different channel. 

See if those few suggestions will improve the matter.

It’s a WiFi setup. I’ll look into those ideas. Thanks